<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title></title>
</head>

<body>
<form id="myform"  method="post" action="#">
    <select name="grade" id="grade">
        <option value="1">1级</option>
        <option value="2">2级</option>
        <option value="3">3级</option>
        <option value="4">4级</option>
        <option value="5">5级</option>
        <option value="6">6级</option>        
    </select>
</form>
<script>


var form = document.getElementById("myform");
var grade = form.elements["grade"];                       

grade.onchange = function(){
	var option = grade.options[grade.selectedIndex];
	grade.insertBefore(option, grade.options[option.index-1]);
}
                
</script>
</body>
</html>
